Effect of Ga+ ion irradiation on the structural and magnetic properties of CoFe/IrMn exchange biased bilayers

Abstract

The effects of focused beam Ga+ ion irradiation on the physical microstructure and magnetic properties of CoFe/IrMn exchange biased bilayers have been investigated by transmission electron microscopy. Only for Ga+ ion doses >1014 ions cm−2 was the microstructure detectably altered with increases in both the bilayer mean grain size and texture being observed. At larger doses (>1015 ions cm−2) radical alterations to the grain morphology and polycrystalline nature of the film were observed including formation of a remarkable needle-like phase at 3×1015 ions cm−2. The magnetic properties and magnetization reversal behavior of the bilayer were studied using the Fresnel mode of Lorentz microscopy. Ga+ ion doses >1013 ions cm−2 were found to progressively reduce the bias field strength and coercivity with the former reaching half original strength at 2×1014 ions cm−2. Higher doses were found to alter the reversal mechanism accompanied by progressive degradation of the magnetic properties. It is likely that the observed magnetic property changes are caused by intermixing of atoms between the various layers.